In the prior art methods for the preparation of physiologically active compounds such as 10-{.beta.-[N-(1,4-diazobicyclo-/4,3,0/-nonanyl)propionyl]}-2-chlorophenot hiazine dihydrochloride and .gamma.-[N-(1,4-diazobicyclo-/4,3,0-/-nonanyl)]propyl-parafluorophenylketo ne dihydrochloride use is made of octahydropyrrolo-/1,2-a/-pyrazine which is produced by reduction of hexahydropyrrolo-/1,2-a/-pyrazin-1-one with lithium alumohydride in the medium of diethyl ether. The starting hexahydropyrrolo-/1,2-a/-pyrazin-1-one is prepared by a multi-stage synthesis from 67 -chlorovaleric acid which comprises bromination of .delta.-chlorovaleric acid in the presence of PCl.sub.3, esterification of the resulting product, followed by condensation with ethylenediamine. This prior art method has disadvantages residing in the necessity of using a hazardous and rarely-available lithium alumohydride, an inflammable solvent as well as the difficulty of preparing the starting hexahydropyrrolo-/1,2-a/-pyrazin-1-one based on the use of .delta.-chlorovaleric acid.
Also known in the art is a method of preparing octahydropyrrolo-/1,2-a/-pyrazine by way of a catalytic dehydration of furan diamine. This prior art method has a disadvantage residing in a complicated character of the process of dehydration of N-tetrahydrofurfurylethylenediamine which is effected in a quartz pipe at a temperature within the range of from 300.degree. to 315.degree. C. over alumina activated with zirconia. This process has another disadvantage residing in a low yield of the desired product, i.e. 30%, and, furthermore, it is very difficult to implement the process on a commercial scale.